1. Field of the Invention
This invention relates to a method and apparatus for inside frosting of tubing and particularly tubing intended for use in endotracheal applications where it is necessary that a suction catheter be passed down an endotracheal tube to remove secretions by suction.
2. Description of the Prior Art
In endotracheal applications, it is frequently necessary that a suction catheter be passed down a larger endotracheal tube. If the inside of the endotracheal tube has a shiny or glossy surface, passage of the suction tube therethrough becomes more difficult. Suction catheters are normally relatively soft and have a tendency to wedge between the walls of the endotracheal tube when being pushed around corners. A frosted surface reduces surface friction where the catheter and endotracheal tube touch.
The present invention is particularly directed to method and apparatus for effecting in a convenient and effective manner the inside frosting of a tube used in such endotracheal applications.
The frosting of tubing, both of the exterior and of the interior walls thereof, is of course known in the prior art. The present invention is directed to an improved method and apparatus for efficiently and effectively frosting the inside of a tube simultaneously with the extrusion forming of that tube, the frosting being accomplished by supplying coolant in a particular manner during the extrusion forming process.
The prior art shows arrangements for extruding tubing and simultaneously supplying cooling air. There are a number of examples in the prior art of arrangements for directing cooling air to both the interior and exterior surface of a tube during the extrusion process in order to achieve a smooth rather than a frosted surface. Thus, normally the prior art provides for directing cooling air or other coolant directly against the surface of the tubing itself and, as indicated above, for a purpose other than securing the frosting of the tubing.
The prior art also discloses an arrangement for cooling an inner die pin to effect frosting of the inside of a tube being extruded. However, in this prior art arrangement the inner die pin is cooled by conduits which are embedded therein and carry cooling fluid to and from a chamber at the forward end of the inner die pin. In this prior art arrangement, variation in temperature differential at the inner die pin is provided only by varying the amount and temperature of the cooling fluid supplied. No provision is made for varying the area at which the cooling fluid is applied. Further, this prior art arrangement is subject to uneven cooling of the inner die pin because of a cool spot at the entry side of the chamber and a warmer spot at the exit side of the chamber. In the applicants' arrangement not only is provision made for varying the area of impingement of cooling air on the inner die pin, but such cooling air is delivered uniformly over the entire inner circumference of the inner die pin to provide uniform cooling thereof. The prior art does not disclose, so far as the applicants are aware, the provision of a method and apparatus for securing inside frosting by cooling an inner die in the manner of the applicants' invention. By the present invention a convenient and effective arrangement is provided for effecting the frosting of the inside surface of a tube.
Accordingly, it is an object of this invention to provide an improved method and apparatus for effecting the inside frosting of a tube, and particularly of a tube used in endotracheal applications, simultaneously with and as part of apparatus for extruding the tube.